1. Field of the Invention
This invention relates to a ceramic which has non-linear voltage characteristics and is suitable for use as an overvoltage protecting resistor and to a method for producing the same.
2. Description of the Prior Art
Heretofore, over-voltage protecting resistors made of a silicon carbide varistor, a selenium varistor, and the like have been widely used practically. However, the over-voltage resistivity of a semiconductor element such as a diode, a transistor, and a thyristor is far lower than that of the ordinary electrical machine or piece of equipment. When protection of the semiconductor element from an over-voltage is desired, a resistor used for that purpose must have the characteristic of a low limiting voltage and the greatest non-linearity for voltage. In this respect, neither a silicon carbide varistor nor a selenium varistor have any significant voltage non-linearity, and furthermore, the limiting voltage of the silicon carbide varistor is high while the loading capability of the selenium varistor is low and the size thereof becomes large. These characteristics are thus the drawbacks of conventional over-voltage protecting resistors. In addition to the above-described resistors, an arrester having series gaps and an arresting tube are known. These are, however, not suitable for the protection of semiconductor elements because of their high limiting voltage.